Refractive errors in the eye can be attributed inter alia to refractive errors in the eye lens or to a sub-optimal surface shape of the anterior and posterior sides of the cornea. The refractive error of the eye lens is usually calculated from the subjectively determined total error of the eye and the refractive properties of the cornea.
According to the known prior art, various methods exist to determine the two surface shapes and the thickness of the cornea.
With a slit lamp microscope, one of the most important exploratory devices in ophthalmology, the cornea can generally be subjected only to a qualitative examination by an ophthalmologist or optometrist. The slit of light projected onto the cornea creates an optical section through the cornea, which is viewed with different zoom levels. Through various methods of lighting (diffuse, direct, focal, indirect, regressed, lateral, etc.) and variable light slit widths, it is possible in addition to the anterior portion of the eye to also inspect the middle and posterior portions of the eye. However, determining the surface shapes and the thickness of the cornea is not possible.
For determining the surface shapes and/or thickness of the cornea, current systems use elaborate measurement and evaluation methods. Some systems are only suitable for such tasks.
For example, a pachymeter is used exclusively for measuring corneal thickness in the human eye. Firstly, the determination of the corneal thickness is relevant for the correct determination of the intraocular pressure by tonometry. Secondly, pachymetry plays a further important role in preparation for various eye surgeries.
Here, the following two different methods are generally used:                non-contact optical measurement (optical coherence pachymeter, OCP) and        determination by ultrasound, wherein a small ultrasound transducer is placed on the cornea.        
In contrast, the ophthalmometer (or keratometer) is an instrument for measuring the surface curvature of the cornea of the eye, as well as determining the corneal curves (keratometry). The instrument allows the measuring of the virtual image and thus a conclusion regarding the curvature of the reflecting surface. Here, a lighted object is placed at a known distance and the reflection of the cornea is observed. This method of measurement is currently used primarily in ophthalmic optics in the fitting of contact lenses, wherein the ophthalmometer is increasingly being replaced by a development thereof, namely the video keratometer.
Another computer-assisted measuring system for the precise measurement of the corneal surface is represented by the keratograph or corneal topographer. Here, the curvature of the cornea, thus the anterior ocular surface, is detected across a large area, which corresponds to a count of approximately 22,000 measurement points. For this purpose, test marks are projected onto the cornea in the form of a ring, and the mirror image thereof is used to calculate the corneal curvature. The curvature distribution can now be calculated from the deviation of these ring images from the ideal spherical shape, and a three-dimensional “map” of the cornea can be determined by conversion of the measurement data.
Modern imaging corneal tomography systems are based, for example, on rotating Scheimpflug cameras or scanning slit systems. Through the combination with Placido discs, the field of imaging, in particular of the anterior segment of the eye, can be significantly improved. These new tomographs create three-dimensional models of the cornea and allow the direct measurement of both corneal surfaces.
The currently available systems have the common disadvantage that they can generally only characterize the anterior portion of the eye and that they are only suitable for such tasks.
The object of the present invention is to further develop or supplement the present ophthalmologic devices such that therewith, in addition to the existing measurement tasks, a determination of the refractive errors in the eye due to a sub-optimal anterior and/or posterior surface shape of the cornea is possible.
This object is achieved by the inventive method for determining refractive errors in the eye that can be traced to a sub-optimal surface shape of the anterior and/or posterior surface of the cornea, in that an OCT volume scan and/or OCT line scan of the anterior segment of the eye is performed, that anterior and posterior surfaces of the cornea are detected from the measured values through edge detection and topographies of refractive errors are determined therefrom.
The proposed method is used for determining refractive errors in the eye, which are due to a sub-optimal surface shape of the anterior and/or posterior side of the cornea. Because the inventive method is based on OCT scans, it thus expands the scope of application of pure standard OCT systems and integrated OCT systems. A prerequisite here is that the OCT systems used are designed for the examination of the anterior ocular segment, which is usually already the case in systems used in ophthalmology. Furthermore, the OCT systems should have different scanning modes, the scan directions of which can be individually customized. Here, the OCT systems may be based both on “time domain” as well as “frequency domain” methods, and in particular also based on a “swept source” system.